Spin down and oscillations in 4U 1907+09: a retrograde disk?

Zand, JJMI
Strohmayer, TE
Baykal, Altan
X-ray observations of the accretion-powered X-ray pulsar 4U 1907+09, obtained during February 1996 with the Proportional Counter Array on the Rossi X-ray Timing Experiment (RXTE), have shown interesting features of which three are: 1) a flare occurred lasting at least a few hours and close to the time of apastron; 2) the spin down rate, when measured since the pulsar discovery in 1983, is within 8% equal to a value of (P)over dot(pulse) = +0.225 s yr(-1), this suggest that the pulsar is in a monotonous spin down mode; 3) transient similar to 18 s oscillations appeared during the flare. The oscillations may be interpreted as Keplerian motion of an accretion disk near the magnetospheric radius. This, and the notion that the co-rotation radius is much larger than any conceivable value for the magnetospheric radius (because of the long spin period), renders it unlikely that this pulsar spins near equilibrium like is suspected for other slowing accreting X-ray pulsars. We suggest as an alternative that perhaps the frequent occurrence of a retrograde transient accretion disk may be consistently slowing the pulsar down. Further observations of flares can provide more evidence of this.


X-ray timing properties of four anomalous x-ray pulsars: 4u 0142+61, 1e 2259+586, 1rxs j170849.0_400910, and 1e 1841_045
Çerri, Danjela; Baykal, Altan; İnam, Sıtkı Çağdaş; Department of Physics (2015)
In this thesis, the detailed X-ray timing characteristics of four Anomalous X-Ray Pulsars (AXPs); 4U 0142+61, 1E 2259+586, 1RXS J170849.0 -400910, and 1E 1841- 045 are presented for glitch free time intervals using data taken by Rossi X-Ray Timing Explorer (RXTE). The pulse arrival times of these AXPs are evaluated by phase coherent timing method. After the removal of the spin-down trend from pulse arrivals, remaining residuals are used for estimation of their noise strengths. Possible correlation of the no...
Recent X-ray measurements of the accretion-powered pulsar 4U 1907+09
in't Zand, JJM; Baykal, Altan; Strohmayer, TE (IOP Publishing, 1998-03-20)
X-ray observations of the accreting X-ray pulsar 4U 1907 + 09 obtained during 1996 February with the Proportional Counter Array onboard the Rossi X-Ray Timing Explorer (RXTE) have made possible the first measurement of the intrinsic pulse period (P-pulse) since 1984: P-pulse = 440.341(-0.017)(+0.012) s. 4U pulse 1907 + 09 is in a binary system with a blue supergiant. The orbital parameters have been solved, which enables us to correct a measurement of P-pulse obtained in 1990 with Ginga for orbital delay ef...
The steady spin-down rate of 4U 1907+09
Baykal, Altan; Alpar, MA; Zand, JI; Strohmayer, T (2001-11-11)
Using X-ray data from the Rossi X-ray Timing Explorer, we report the pulse timing results of the accretion-powered, high-mass X-ray binary pulsar 4U 1907 + 09, covering a time-span of almost two years. We measured three new pulse periods in addition to the previously measured four pulse periods. We are able to connect pulse arrival times in phase for more than a year. The source has been spinning down almost at a constant rate, with a spin-down rate of (nu) over dot = (- 3.54 +/- 0.02) x 10(-14) Hz s(-1) fo...
Short-term pulse frequency fluctuations of OAO 1657-415 from RXTE observations
Baykal, Altan (2000-04-11)
We present new X-ray observations of the high-mass X-ray binary (HMXRB) pulsar OAO 1657-415, obtained during one orbital period (10.44 d) with the Rossi X-Ray Timing Explorer (RXTE). Using the binary orbital parameters, obtained from Burst and Transient Source Experiment (BATSE) observations, we resolve the fluctuations in the pulse frequency at time-scales on the order of 1 d for the first time. Recent BATSE results by Baykal showed that OAO 1657-415 has spin-up/down trends in its pulse frequency time seri...
Recent Spin Rate Measurements of 4U 1907+09
Sahiner, S.; İNAM, SITKI ÇAĞDAŞ; Baykal, Altan (2010-08-06)
In this study, X-ray spectral and pulse timing analysis of the high mass X-ray binary (HMXB) pulsar 4U 1907+09, based on the observations with RXTE are presented. Spin rate measurements indicate a new spin-down episode with a rate close to the previous steady spin-down rate. Orbital phase resolved spectroscopy reveals that the Hydrogen column density varies through the orbit reaching to its maximum value just after periastron. A slight spectral softening with increasing luminosity is aslo observed.
Citation Formats
J. Zand, T. Strohmayer, and A. Baykal, “Spin down and oscillations in 4U 1907+09: a retrograde disk?,” NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS, pp. 224–227, 1999, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/46585.